Remove unnecessary dict.keys() method calls (api)

Since iter(dict) is equivalent to iter(dict.keys()), it is unnecessary
to call the keys() method of a dict, the dictionary itself is enough
to be referenced. The shorter form is also considered to be more
Pythonic.

This patch removes the unnecessary dict.keys() method calls in api.
This is a part of a larger patch series that removes dict.keys()
method calls.

TrivialFix

Change-Id: I29000f1f05b90d70109fa01393e97e1ebf450c63

watcher/api/scheduling.py

@@ -42,7 +42,7 @@ class APISchedulingService(scheduling.BackgroundSchedulerService):
         services = objects.service.Service.list(context)
         for service in services:
             result = self.get_service_status(context, service.id)
-            if service.id not in self.services_status.keys():
+            if service.id not in self.services_status:
                 self.services_status[service.id] = result
                 continue
             if self.services_status[service.id] != result: